| The Songxi Ag-Sb deposit, which is located in the northwest of Guangdong province of China, is formed in the northen margin of Zaigangshang volcanic fault basin developed in the Yongding-Meixian Paleozoic geotectogene. The extension affecting this region in late Tertiary and early Jurassic period was followed by a regional compression of middle Jurassic. During late Jurassic, this region was again in an extensional environment which resulted in the formation of Mesozoic volcanic basins and large scale volcano-intrusive complexes of acidic composition. Songxi Ag-Sb deposit formed in the end of Jurassic and the beginning of Cretaceous, and was genetically related to the late Jurassic magmatism. The ore of Songxi Ag-Sb deposit is developed in the Jinji formation of early Jurassic period and is hosted by a suite of basaltic volcano-sedimentary rocks under which there is a sheet of basalt. The concentrations of metal elements in Jinji formation outside the mining area is similar to or lower than the averages in sedimentary rocks all over the world. This fact challenges the argument that the metals in Songxi Ag-Sb deposit is mainly from Jinji formation and is similar to the elemental distribution around an epithernial deposit where ore forming metals are leached by convecting solution. The ore is emplaced via metasomatism and filling mainly along the faults that trend dominately in northeast direction with a few of EW-trending. Because the occurrence of the NE-trending faults is close to that of the strata on the NE limb of the anticline developed in the mining area, the ore veins have previously been regarded to be stratabound. On the SW limb of the anticline, however, the veins filling along the NE-trending faults clearly cut the strata and can intrude the middle Jurassic Zhangping group, providing strong evidences that the mineralization in Songxi Ag-Sb deposit is developed as ore forming fluid flow in fractures. In addition, the enrichment center of Ag and Sb mineralization halo distributes along the axial of the anticline, also confirming the importance of structure in controlling the mineralization. The ore is characterized by veinlet structure, net-veined structure and comb structure, and the gradual outward transformation of ore structure from veined via net-veined and veinlet-disseminated to disseminated is common. These characteristics in ore fabrics and the occurrence of cryptoexplosive breccia are strong evidences that Songxi Ag-Sb deposit is a hydrothermal deposit. In addition to sulfide minerals, Songxi Ag-Sb deposit is characterized by a group of sulfosalts that are rich in Ag, Sb and As. Ore zoning has been recognized both vertically and horizontally. The upper part is Ag-Sb mineralized zone; the middle part is Ag mineralized zone with a little degree of Au, Pb and Zn enrichment, and minor enrichment of Cu and Mo occur in the lower part. The wall rock alteration includes silicification, pyritization, sericitization, carbonation, with siliciflcation and pyritization at the mineralization center and carbonation to the outmost. On top of the ore deposit, there is a silicated cover that formed during the acidic leaching. Framboidal pyrite with lamellar structure is unique of sedimentary pyrite in Songxi. This kind of pyrite is genetically related to the basaltic volcanism in early Jurassic period and, as compared with the pyrite in the ore-veins, is rich in highly incompatible elements such as Co and Ni, and poor in Ag and Sb. This fact demonstrates that the Jinji formation can not be the major source of the ore-forming metals of Songxi Ag-Sb deposit. In addition, N...
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